update-drawable

Arguments:
drawable

Causes drawable (an instance of the drawable class) to be redisplayed, either by calling the on-redisplay function or by causing the image in the bitmap-stream associated with drawable to be displayed.

An application may call update-drawable on a drawable that uses an on-redisplay function
that draws its drawing based on parameters that may change over
time. This forces the on-redisplay function
to be called in order to draw the current version of its drawing when
the control may not otherwise need to be redrawn.

If done in rapid succession, this can produce animation effects,
especially if the use-bitmap-stream property is
currently turned on in order to eliminate the flashing that is
produced when erasing and redrawing directly on the visible window.